Recovery of waste sulphuric acid liquors



Feb. 5, 1946. J. M. OSHAUGHNESSY 2,394,470

RECOVERY OF WASTE SULPHURIC ACID LIQUORS Filed June a, 1944 sSheets-Sheet 1 JZzq. 1.-

WASTE ACID LIQUQR CONTAIN ma Fe s 0 TREATMENT(NEUTRALIZATION) Fe 5 ANDH1504.

SOLUTION OF FeSO REACTON MAKE-UP ALKALINE EARTH M ETAL SULFATEFILTRATION PETROLEUM COKE FILTRATE MIXED PR'ECIPITATE TO WASTE OF F85AND ALKALINE EARTH METAL SULFATE H25 (WHEN ALKALINE REDUCING CALCINATIONEARTH METAL is C LEACHING soumon OF ALKALINE EARTH METAL sum DEonuvoaosumoe F85 H CAKE EXCESS REMOVED To ROASTER FOR PRODUCTION OF 50OR TREATED WITH ACID TOEVOLVE ms flMfSMlC/[AEZ omwfimsy IN VEN TOR.

. ATTORNEY Feb/5,1946.

J. M. O SHAUGHNESSY RECOVERY OF-WASTE SULPHURIC ACID LIQUORS Filed June8, 1944 jfzq. Z.

3 Sheets-Sheet 2 PRECI PlTATED Fe 5 soumon OF Peso;

1; I Y I I l N a z s R EAC T o N l l I l PI LTRATION I Q l 1 SOLUTION OFM62504 Fe 5 PRECIPITATE I l OPTlONAL LONCENTRATION AND EXCESS FeSREMOVED TO I PROCESSING m ANHYDROUS M 50 ROASTER FOR PRODUCTION OF 502wmcn MAY BE CONVERTED TO na s ORTREATED wrm ACIDTO EVOLVE H 5flMESMIGHAEL OJJMUQHESS Y IN VEN TOR.

' TTORZV EL Feb. 1946. J. M. OSHAUGHNESSY 2,394,470

RECOVERY OF WASTE SULPHURIC AC ID LIQUORS Filed June 8, 1944 3Sheets-Sheet s jfzq. 5.

WASTE ACID LIQUOR MIXED PRECIPITATE OF NTA NIN F S TREATM R CO ANID 5 54o4 ENT(NEUT ALIZATION) Fes AND B51504 N EXCESS PETROLEUM COKE FILTRATIONFILTER CAKE: REMAINING FeS AND SOLUTION OF F6504 ALL 86.504.

REACTION LEACHING FILTRATION F 5 MIXED PRECIPITATEOF F FeS AND 8&50

$OLUTION OF 865 FILTRATE TO WASTE I TO ROASTER TO PRODUCE $0 OR TREATEDWITH ACID TO EVOLVE H 8 JILMI'SMICHAZL OSJ/AUGIJWZJSY IN VEN TOR.

BY I I ATTORNEY the recovery of hydrolysis Patented Feb. 5, I946 umrsoSTATES PATENT orrlcs STE SULPHURIC A LIQUORS RECOVERY OF WA James M.OShaughnessy, Woodbridge,

' signor to National Lead Company, New

.N. Y., a corporation New Jersey Application June 8, 1944, Serlal No.539,332

13 Claims.

The present invention relates to a method for the treatment ofindustrial liquors containing,

sulphuric acid and constitutes a practical and economical means for therecovery of the sulphuric acid content of such liquors. Where suchindustrial. sulphuric liquors contain, in addition to sulphuric acid,other valuable constituents,

such as iron, or titanium, or both, the present invention provides.means for the recovery oi such other constituents as well as thesulphuric acid content.

The principal object of the present invention is to provide a practicaland economical method for the recovery of the sulphuric acid content ofindustrial sulphuric acid liquors. Another important object of thepresent invention is the recovery of valuable constituents, other thansul-, v phuric acid, which may be contained in such liquors. Whensulphuric acid liquors containing titanium, ior instance, a sulphuricacid solution of llmenite, are treated according to the presentinvention, there is obtained a precipitate of hydrous titanium oxidewhich is especially suitable for further processing to useful titaniumcompounds, such as titanium pigments, especially vpigmentary titaniumdioxide of the rutlle moditreated with iron sulphide is subjected to areducing treatphide to convert the iron sulphate fication. Accordingly,a third important object I of the present invention is to provide meansfor obtaining hydrous titanium oxide especially suit- .able for furtherprocessing into titanium dioxide pigments.

The present as waste from various industrial processes, for example,from the pickling of iron and steel, from the hydrolysis of sulphuricacid solutions of ilmenite,or from the treatment of sulphuric acidsolutions obtained by treatment of minerals, such invention is adaptedfor the treatment of sulphuric acid liquors obtained either I tionwherein the acid liquor is ment and the iron sulphide separated from theresulting alkaline earth metal sulphide, both of which arethen'reusedinthe process. i

Fig. 2 illustrates the .use'of an alkali metal sulto iron sulphide. Y

Fig. 3 illustrates an embodiment of the inventreated with a mixture ofiron sulphide and alkaline earth metal sulphate obtained from a previousoperation of the process, v I

The' foregoing relation to several preferred embodiments oi. the

- present invention."

In the first step at'le'ast enough iron' sulphide will be added to thesulphuric acid liquor either as such (Fig.1) or asia mixture wlth'alkaline earth sulphate obtained from previous operation of theprocess (Fig.3), inorder substantially completely to neutralize the sulphuric acidcontent of the liquor, it being understood that when treating a liquorcontaining titanium the sul-- pburic acid content will include the freeacid as 'well as the acid regarded as combined with the as, titaniierousores. It is especially adapted for contain, in addition to sulphuricacid, hydrochloric mother liquors which acid, the presence of whichprevents, .due to its I "."highly corrosive nature, the eil'ective andeconomic recovery of the sulphuric acid by the usual rior art methods.

The several essential steps comprising the procv5 es of the presentinvention are combined in such manner as to constitute a cyclicalprocess in which the reagents employed are continuously reutilized 101'the treatment of sulphuric acid liquors, the end products thereof beingsulphuric acid and possibly also the other valuable constituents, forexample, iron or titanium compounds, or both.

The essential steps above referred to comprise? titanium. The ironsulphide may be added to the liuqor in any convenient form, either dryor, as is preferred, in the form of awet flltercake. As a result of theaddition of the iron sulphide, the sulphuric'acid content of the liquoris converted to iron sulphate whith remains in solution and hydrogensulphide gas is evolved which is collected for subsequent conversion tosulphuric acid. This first step may be carried out at room temperatureor, if desired, more elevated temperatures which may be found ing orcompleting the conversion. A very convenient method for carrying out theiron sulphide treatment especially when earth metal sulphate is to leachthe iron sulphide material with the acid liquor according to the (a) Thetreatment of the sulphuric acid liquor 5 welL-known counter-currentprinciple until it has the hydrogen sulphide steps will now be describedin p helpful in acceleratit contains alkalineand washed.

' been converted to iron sulphate and as such dissolved in the liquor.

When the acid liquor contains titanium, there will be obtained after theiron sulphide treatment a precipitate of hydrous titanium oxide.According to the present invention, this hydrous titanium oxide afterproper adjustment of, the

pH to obtain a illterable product is separated from the mother liquorcontaining ironsulphate,

which may be used for the preparation of a hydrous titanium oxideconvertible upon vcalcinetion to pigmentary rutile titanium dioxide. Inthe second step the iron sulphate contained This conversion is carriedout with a metal sul-.

- phi'de capable of converting the iron sulphate to iron sulphide. Asregards the metal sulphides useful in practicing thepresent. inventionany sulphide which stands above iron in motive series may be used.

According to the preferred method the metal sulphide which is to beadded to the iron sulphate solution may beeither an alkaline earth-metalsulphide, or hydrosulphide'-(Figs. 1 and 3), e. g.

the sulphides or hydrosulphides-oi' calciumand barium, or with a solublealkali metal sulphide, e. g. sodium or potassium sulphide '(Fig.-2)'. A

According to those embodiments of the present all solution, to convertsubstantially all of the ironsulphate to ironsulphide. Asa result ofthistreatment, there is obtained 'a precipitate of iron;

sulphide anda solution of alkali metal sulphate.

invention which include the treatment of the iron sulphate liquor withalkaline earth metal sulphide or hydrosulphide therewill be generally 4added to the iron sulphate liquor atleast a sufv flcient amount ofalkaline-"earth metal sulphideiilirom the alkali metal sulphatesolution, to i- 1m x or hydrosulphide to convert-'substantially come.

pletely the iron sulphate to iron sulphide. From f this treatment therewill be obtained a mixed precipitate of iron sulphide. and alkalineearth metal sulphate.

eflected in several ways. As illustrated in Fig. 1,

r it may be subjected to a reducing calcination to sulphide forconversion of iron sulphate to ironsulphide. Alternatively, asillustrated in Fig. 3, the mixed precipitate of alkaline earth metalsul-, phate and iron sulphide may be added in its entirety to a measuredamount of additional acid liquor and after complete neutralization theexcess iron sulphide and the alkaline earth metal sulphate may beseparated by filtration from the resulting iron sulphate liquor. Thealkaline earth metal sulphate together with the residual iron sulphidemay then be subjected to a controlled reducing calcination in order toobtain a' mixture of alkaline earth metal sulphide and iron sulphide.Another useful alternative, particularly for the treatment of acidliquors which do not contain any substantial amounts of titanium,contemplates the utilization of a portion of the mixed precipitate ofiron sulphide and alkaline earth metal sulphate containing sufficientiron sulphide for the neutralization of theacid, in which case the ironsulphate liquor re- 75 It may be subsequentlyv further" in the motherliquor is converted to iron sulphide.- v

the electro- I The reutilization of the iron sulphide in this mixturefor the treatment of 'an additional quantity or acid liquor may besulting therefrom will contain suspended alkaline earth metal sulphatewhich can be easily removed from the liquor as by decantation,filtration, etc.

The alkaline earth metal sulphateinay thenbe 5 subjected to a reducingcalcination for conversion to sulphide, either separately orin'admixture with additional precipitate of iron sulphide and separatethe iron sulphide from the soluble I barium sulphide, in which case theiron sulphide liquor and the solution of barium sulphide --uti-' lizedfor the treatmentof the resulting-iron sulphateliquor. When the alkalineearthflmetal' sulphide is calcium sulphide obtained by the reducingcalcination of either calcium sulphate it seli'or the mixture ofcalciumsulphide and iron sulphide, it is preferable, since calciumsulphide is substantially insoluble in water. to treat the calciumsulphide in water' suspension with hydro gen sulphide, preferably undervpressure, in order to form the calcium hydrosulphide in which form it isutilized for the treatment of additional iron sulphate liquor. The useor calcium sulphide, or slurried in water, is however within the scope.metal sulphide is em- Q I ployed in the practice of the presentinventiom'j I of this invention.

When a soluble alkali as illustrated in Fig. 2, it will generally befound "The precipitated-iron sulphide is next removed stance, bydecantation or, filtration, or both.

This iron sulphide is then available folf treati'ns additional amountsof sulphuric acidliquor. It

will be understood, however, that in the practice of the presentinvention when the startingmaterial itself contains iron, the ironsulphide which '1' will ,be recovered by separation from the alkalimetal sulphate solution will bein excess of that required to convertthesulphurlc acid content I ,of an additional equal quantity of acidliquor.-- The excess iron sulphideis "bled oiT'and may, be processed torecover the sulphur content thereof as sulphur oxygen gases which may'be embodiment of the invention, may be evaporated in order to recoverthe alkali metal sulphate as a solid which in turn may be subjected to-acontrolled reducing calcination in order'to'conphide, which 'in turn isused to treat'iurther I quantities of iron'sulphate mother liquor. Itwill be understood that should the conversion of alkali metal sulphateto alkali metal sulphide prove more costly than the purchase of freshalkali metal sulphide, the solution of alkali metal sulphate may bedisposed of as such and -iresh alkali metal sulphide used to treat thefurther present invention as represented by Fig. 2 may is reutilized forthe treatment of additional acid used for the production of sulphuricacid; The alkali metal sulphate solution, according to this vertthealkali metal sulphate to alkali metal sulquantities of iron sulphateliquor, all without departingfrom the scope of the present invention. Itis to be noted that the embodiment of the 7 include an evaporation stepin which a consid-' erable amount of water has to be removed. Thisobtained as mother o! a sulphuric acid had the i'ollowing analysis:

\ The hydrogen treatment was collected and I ing was burned to sulphur"until the pH reached hours at about 1000 C. in

Y autoclave. Hydrogen sulphide was evaporation may prove rather costlyin practical applications of the present invention and it, therefore,may be found more economical to employ those embodiments oi! the presentinvention as represented by Figs. 1 and 3 wherein an alkaline earthmetal sulphide is employed for the conversion Of the iron sulphate toiron sulphide.

The following examples will more particularly illustrate, withoutlimiting, the present invention.

Exmu I (Illustrating the use of calcium hudrosulphide,

, according to Fig. 1)

' Two liters of an industrial liquor from the hydrolysisilmenitesolution and analyzing as follows: I

"s ecies gravuy: 1.1aa 7 mean (g. p. 1.) 124 FeSO; (g. p. l.) 110- wetground commercial ferrous sulphide of about 90% FeS. The resultant 2.230liters o! liquor Specific gravity 1.246 F8304 (g. p. 1.) 271 PH 3.9

4 about 119 grams per liter of calcium sulphhydrate about 7.0. A mixedpre cipltate of calcium sulphate and iron sulphide was obtained whichwas separated from the supernatant liquor by filtration. The filtrate.was found to be free from iron salt.

The mixed precipitate of calcium sulphate and iron sulphide was mixedwith 0.270 kilogram of granular petroleum coke and roasted for three arotary furnace. About 98.6% oi the calcium sulphate was con- The mixtureof calcium sulphide and iron sulphide was suspended in water and placedin an through this suspension under a pressure of about 5 lbs. persquareinch for about two hours. This treatment effected a conversion andsolubilization of about 97.5%0! the calcium sulphide as calciumsulphhydrate, after sulphuric acid liquor mum-s l1 (Illustrating.treatment of waste acidwith mixed 'FeS-BaSOl precipitate according tol'ia. 3)-

2.230 liters of iron sulphate solution Specific gravity F8804 (g. p.l.)... P

.obtained as described under Example I were treated with a hotconcentrated solution of barium sulphide in stoichiometric amount. Alteragitation to complete the reaction at a pH of about 7.0 the mixedprecipitate of barium sulwere treated with 0.250 ldlogram, dry basis, of

after which the iron sulphate liquor was sepa- 'rated by filtration fromthe mixture of the excess of iron sulphate.

obtained after .drydioxide for subsequent were obtained .in this vertedto calcium sulphide while the iron sulphide remained unchanged.

circulated which the iron sulphide was separated irom the solution ofcalcium;

sulphhydrate.

The recovered iron sulphide was about 0.341 kilogram, 0.225 kilogram ofwhich were used for the treatment of additional 2.000 liters ofsulphuric acid hydrolysis mother liquor, while the 0.116 kilogram ofexcess FeS was roasted to recover the sulphur values as S0: forsubsequent conversion to sulphuric acid.

The solution of calcium hydrosulphide contained about 119 g. p. l. andwas employed for the treatment of about 2.150 liters of iron sulphateliquor obtained as above described.

phate and iron sulphide was filtered and washed. .A filter cakecontaining 0.926 kilogram of Ba804 and 0.348 kilogram of FeS wasobtained corresponding to one hundred per cent conversion.

The filtrate was clear and was found to contain only a trace of solubleiron salt. 7

2.000 liters of sulphuric acid hydrolysis mother liquor of the samecomposition as that used in Example I was then treated with themixedprecipitate of FeS" and BaS04 obtained in the preceding step. Theneutralization was carried out.

countercurrently in two steps and continued until a completeneutralization had taken place,

and barium sulphate and the filter Specific gravity F8804 (g. p. l.) 224manner, equal to 0.604 kilogram-of F6804. 0.225 kilogram of ironsulphide were consumed in the reaction, while 0.123 kilogram of excessmake-up barium sulphate in the form of ground barytes and withgranulated petroleum coke to give a mixture of the followingcomposition:

Kilograms FeS 0. 123 139.50 0.926 Barytes 0. 103 Petroleum coke 0.800

The mixture was dried and then roasted in the absence of air at 1000 C.for about 3 hours to reduce the barium sulphate to barium sulphide. Thecharge was allowed to cool after which by countercurrent leaching withhot water 0.674 kilogram oi! BaS, equivalentto aboutper cent conversion,were obtained in solution. This amount is slightly in excess of thatrequired for the double decomposition of the 0.604 kilogram of ferroussulphate (2.700 liters oi! 224 g. 1. R804) obtained in the precedingoperational cycle and was usedto repeat the entire process.

The residue from the barium sulphide leaching was analyzed. The ironsulphide was found to be unchanged and only a small amount ofunconverted barium sulphate was present in the residue, thenon-leachable portion of the barium being predominantly present in theform of barium carbonate. This residue may be processed for its bariumand sulphur values by known means with all the barium eventuallyconverted to sulphate I iron sulphide and 0.926 kilo-' gram of bariumsulphate were collected in the (Illustrating the described in ExamplelI.

"illustratin the use oi al for return to the process for conversion tobarium sulphide, in which case it becomes unnecessary to;

sulphate for balancing add any make-up barium the cyclic -process.

Exams: II!

no to Fly. 1)

use of barium sulphide, accord of hydrolysis mother liquor with ironsulphide was treated with 0.303 kilogram of barium'sulphide in themanner described under Example 11. The mixed precipitate of bariumsulphate and I iron sulphide was combined with abo'utOJOll kilo-'-aaeacro Y liquors containing sulphuric acid which com- I prises addingto such liquor iron sulphide to convert the sulphuric 'acidcontent ofsaid liquor-v to iron sulphate, collecting the hydrogen sulphide gasevolved during the conversion of sulphuric acid and to iron sulphateconverting by metathesis the iron sulphate to iron sulphide andutilizingthe same for the treatment of additional sulphuric acid liquor. I

2. Method for the treatment of industrial liquors containing sulphuricacid which comprises adding to such liquor iron sulphide in an amountsuincient substantially completely to convert the,

. sulphuric acid-content of said liquor to iron sulgram of granularpetroleum coke and-roasted for about three hours at about 10000. Thebar-' ium sulphate was substantially completely con- 1 verted to bariumsulphide while the ironsulphide wremained unchanged. 1 r Thebariumsulphide was separated from the iron sulphide by leaching with hot waterto ob-' tain a solution of barium sulphide in the manner Therecoverediron sulphide was used for the treatment of additional sulphuric acidliquor and v the barium sulphide solutionfor the treatment of additionaliron sulphate solution in the manr er describedinExample I. 1 n

J). vr IV A cording toFig. 2)

One liter of iron sulfate solution equal to 0.270 kilogram of FeSOrobtained as described under Example I, was treatedwith 0.139 kilogram ofNazism the form of a hot concentrated solution under agitation. Atcompleted conversion at a. pH- of about 7.0 the iron sulphideprecipitate,v equal to0.156 kilogram of FeS,-was filtered and washed.The filtrate, containing 0.253 kilogram of sodium sulphate freefromlron, was concentrated and evaporated to dryness-to produce anaiumsulphate back to sodium sulphide was achydrous sodium sulphate.Conversion of the so-' alt metal sulphide, ac

phate, collecting the hydrogen sulphide gas,

evolved during the conversion of sulphuric acid to iron sulphate andoxidizing the same to -sulphuric acid, adding to the-residual solutioncon- 1 taining the iron sulphate a metal sulphide which stands aboveiron in the electromotive series-in an amount suincient'substantiallycompletely t convert the iron sulphate to iron sulphide. and

utilizing the resulting iron sulphide for the treatment of additionalsulphuric acid liquor.

3. Method for the treatment of industrial liquors containing sulphuricacid which comprises adding to such liquor iron sulphide in an amountsufllcient substantially completely to convert the sulphuricacidcontent'oi" said liquor to iron sulphate, collecting the hydrogensulphide gasevolved during theconversion of sulphuric acid to ironsulphate and oxidizing the same to' '1 sulphuric acid. addingtotheresidual solution 1 containing the iron sulphate a soluble alkalimetal sulphide in an amount sufllcient substantially completely toccnvertthe ironsulphate to iron sulphide,separating the precipitatediron sulphide from the residual alkali .metal sulphate l I solution andutilizing the resulting iron sulphide treatment or additional "sulphuricacid;

for the.

liquor.

complished by mixing with v0.100'k1l0sram of granulated petroleum cokeand roasting for about 3 hours at 850-900 C. in the absence of air; Theroasted material was leached with hot Water to extract the sodiumsulphide. 'I'he so lution obtained contained 0.125 kilogram sodiumsulphide equal to about 90 percent of the original sodium sulphatepresent as well as some sodium carbonate and a small amount ofunconverted sodiumsulphate. w o

the 0.158 kilogram pro-' duced were returned to the process forneutralization of a new portion of acid liquorwhile thefl 0.109 kilogramFeS of excess iron sulphide equal to 0.047kilogram'FeS were availablefor processing forreclamation on itssulphur values by roasting to 80s.or by other,

l ne foregoing thereof which are within the skill of the art. Forinstance, if desired, the'invention may be operated in suchmanner thatneutralization of the waste acid liquid is carried out in several steps,or neutralized in one or more steps with an excess of iron sulphidewhich is then treated with description of the present invention has beengiven for illustrative purposes. only and the appended claims areintended to'; embrace all embodiments and modifications of iron sulphate4. Method for; the treatmentoi industriala. iquor containing sulphuricacid which, comprises adding to such liquor iron sulphide in an amount.1 I sufiicient substantially'completely to-convert'tlie sulphuric acidcontent'otsaid liquorto iron su.l-

phate, collecting .thelihydrogen "sulphide g jgi; evolved during theconversion of sulphuric acid}. to iron sulphate and oxidizing the sameto sulphuric acid, adding to the residual solution con.-, ,taining theiron sulphate a soluble alkali metal sulphide in an amount sufllcientsubstantially I:

completely to convert the iron sulphate to iron sulphide, separating theprecipitated iron sulphlde from the residual alkali metal sulphate s0-lutionandutiiizing the resulting iron sulphidefor thetreatment ofadditional sulphuric-acid liquor, separating the alkali metal sulfateasa'.v solid from the residual alkali-metal sulphate solution andheating the solid alkali metal sulphate under reducing conditions toreduce the same to alkali metal sulphide and utilizingfthe resultingalkali metal sulphide for the treatment of addi-gtional iron sulphatesolution.

containing sulphuric acid which comprises adding to such liquor ironsulphide in an amount sumcient substantially completely to convert thesul- 5. Method according to claim 3 wherein the alkali metal saltemployed for the conversion to iron sulphide is sodium. sul- 4 whereinthe phuric acid content of said liquor to ii :a sulphate, collecting thehydrogen sulphide gas evolved during the conversion of sulphuric acid toiron sulphate and oxidizing the same to sulphuric acid, adding to theresidual solution containing the iron sulphate a compound selected fromthe group consisting of the sulphides and sulphydrates of the alkalineearth metals in an amount suflicient substantially completely to convertthe iron sulphate to iron sulphide, utilizing the mixed precipitate 01iron sulphide and alkaline earth metal sulphate for the treatment ofadditional sulphuric acid liquor and after the said treatment separatingthe precipitated alkaline earth metal sulphate from the residual ironsulphate solution.

8. Method for the treatment of industrial liquors contaning sulphuricacid which comprises adding to such liquor iron sulphide in an amountsuillcient substantially completely to convert the sulphuric acidcontent of said liquor to iron sulphate, collecting the hydrogensulphide gas evolved during the conversion of sulphuric acid to ironsulphate and oxidizing the same to sulphuric acid, adding to theresidual solution containing the iron sulphate a compound selected fromthe group consisting of the sulphides and suiphydrates of the alkalineearth metals in an amount sufiicient substantially completely to convertthe iron sulphate to iron sulphide, utilizing the mixed precipitate ofiron sulphide and alkaline earth metal sulphate for the treatmentot'additional sulphuric acid liquor and alter the said pletely toconvert the iron sulphate to iron sulphide. heating the mixedprecipitate of iron sulphide and-alkaline earth metal sulphate underreducing conditions to convert the alkaline earth metal sulphate toalkaline earth metal sulphide,

separating the iron sulphid from the alkaline earth metal sulphide andutilizing the iron sulphide for the treatment of additional sulphuricacid liquor and the alkaline earth metal sulphide for the treatment ofadditional iron sulphate s0- lution.

11. Method for the treatment of industrial liquors containingsulphuric'acid whichcomprises tion containing the iron sulphate in anamount treatment separating the precipitated alkaline earth metalsulphate from the residual iron sulphate solution, heating the separatedalkaline earth metal sulphate under reducing conditions to convert thesame to alkaline earth metal sulphide and utilizing the said sulphidefor the treat-- ment of additional iron sulphate solution.

9. Method for the treatment or industrial liquors containing sulphuricacid which comprises adding to such liquor iron sulphide in an amountsumcient substantially completely to convert the sulphuric acid contentor said liquor to iron sulsuflicient substantially completely to convertthe iron sulphate to iron sulphide, heating the mixed precipitate ofiron sulphide and barium sulphate under reducing conditions to convertthe barium sulphate to barium sulphide, leaching the barium sulphidefrom the iron sulphide and utilizing the iron sulphide for the treatmentof additional sulphuric acid liquor and the solution of barium sulphideior'the treatment of additional iron 1---' phate solution. 1

12. Method for the treatment 01' industrial liquors containing sulphuricacid which comprises adding to such liquor iron sulphide in an amountsuflicient substantially completely to convert the sulphuric acidcontent 01' said liquor to iron sulphate, collecting the hydrogensulphide gas evolved during the conversion 01' sulphuric acid to ironsulphate and oxidizing at leaast a part of the same to sulphuric acid,adding calcium sulphydrate to the residual solution containing the .ironsulphate in an amountsuihcient subphate, collecting the hydrogensulphide gas evolved during the conversion of sulphuric acid to ironsulphate and oxidizing at least a part of the some to sulphuric acid,adding to the residual solution containing the iron sulphate a compoundselected from the group consisting of the sulphides and sulphydrates ofthe alkaline earth metals in an amount suflicient substantiallycompletely to convert the iron sulphate to iron sulphide, heating themixed precipitate of iron sulphide and alkaline earth metal sulphateunder reducing conditions to convert the alkaline earth metal sulphateto alkaline earth metal sulphide, separating the iron sulphide from thealkaline earth metal sulphide and utilizing the iron sulphide for thetreatment of additional sulphuric acid liquor.

10 Method tor the treatment of industrial liquors containing sulphuricacid which comstantially completely to convert the iron sulphate to ironsulphide, heating the mixed precipitate of iron sulphide and calciumsulphate under reducing conditions to convert the calcium sulphate tocalcium sulphide, treating the mixedsulphides with water and hydrogensulphide to convert the calcium sulphide to soluble calcium sulphydrate,separating the iron sulphide from the solution of calcium sulphydrateand utilizing the iron sul phide for the treatment oi. additionalsulphuric acid liquor and the solution or calcium sulphydrateo for thetreatment or additional iron sulphate liquor.

13. Method for the treatment of industrial liquors containing sulphuricacid and titanium which comprises adding to such liquor iron sulphide inan amount sufficient substantially completely to convert the sulphuricacid content of said liquor to iron sulphate, separating hydroustitanium oxide precipitated during the conversion 0! the sulphuric acidto iron sulphate, collecting the hydrogen sulphide gas evolved duringthe said conversion and oxidizing the same to sulphuric acid, adding tothe residual solution containing the iron sulphate a metal sulphidewhich stands above iron in the electromotive series in an amountsumcient substantiall completely to convert the iron sulphate to ironsulfide and utilizing the resulting iron sulfide for the treatment ofadditional acid liquor.

J M. OSHAUGHNESSY.

